Variations in leaf functional traits of Stipa purpurea along a rainfall gradient in Xizang, China

doi:10.3724/SP.J.1258.2012.00136

Abstract

Abstract:

Aims Stipa purpurea is the dominant species in alpine arid and semi-arid grasslands on the Tibetan Plateau. Our objectives are to determine if this species exhibits a strategy shift in its specific leaf area (SLA) to nitrogen (N) concentration relationship along a rainfall gradient and to detect possible effects of environmental factors on related leaf traits.
Methods We investigated variations in leaf traits of S. purpurea associated with climatic and soil factors along an east-west transect with a rainfall gradient (69-479 mm) but similar altitudes (4 300-4 700 m). Five locations from east to west are Damxung, Namco, Gêrzê, Mount Qomolangma and Rutog. We measured SLA, mass- and area-based leaf N concentration (N_mass, N_area), leaf density and thickness and soil total N along the transect.
Important findings In pooled data, SLA and N_mass varied little with the growing season mean temperature and precipitation and the soil total N concentration. The SLA-N_mass relationship in S. purpurea did not shift between the semi-humid areas (ratio of rainfall to evaporation > 0.11) and the arid and semi-arid areas (ratio < 0.11), although there was a positive correlation between SLA and N_mass across the five locations. Variation in SLA was mainly determined by leaf density in the semi-humid areas and by leaf thickness in the arid and semi-arid areas; both were negatively correlated with SLA. With increasing temperature or declining precipitation, leaf density decreased and leaf thickness increased, leading to non-significant relationships between SLA and climatic factors. The increase of leaf density in the semi-humid areas was correlated with the increase of N_area, but the increase of leaf thickness in the arid and semi-arid areas did not lead to change of N_area, resulting in unchanged N_area along the rainfall gradient. A positive correlation was detected between aboveground biomass and N_area in S. purpurea, indicating that increased N_area may increase plant productivity. Our findings suggest that alpine plants in arid and semi-arid areas may maintain a constant N_area by increased leaf thickness in order to achieve a similar photosynthetic productivity and water use efficiency compared to the relatively humid areas. The relative impacts of leaf density and leaf thickness on SLA shifted between the semi-humid areas and the arid and semi-arid areas, which may provide insight in detecting the threshold of water limitation in alpine grasslands.

Key words: leaf density, leaf nitrogen concentration, leaf thickness, specific leaf area, Stipa purpurea, strategy shift

HU Meng-Yao, ZHANG Lin, LUO Tian-Xiang, SHEN Wei. Variations in leaf functional traits of Stipa purpurea along a rainfall gradient in Xizang, China[J]. Chin J Plant Ecol, 2012, 36(2): 136-143.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2012.00136

https://www.plant-ecology.com/EN/Y2012/V36/I2/136

Figures/Tables 7

Table 1 Locations and climatic factors of study sites

研究地点 Study site	纬度 Latitude (°)	经度 Longitude (°)	海拔 Altitude (m)	年平均气温 AT (℃)	生长季平均气温 GST (℃)	年降水量 AP (mm)	生长季降水量 GSP (mm)	年降水量/年蒸发量 Ratio of rainfall to evaporation
当雄 Damxung	30.50	91.05	4 480	1.66	9.78	479	402	0.25
纳木错 Namco	30.77	90.98	4 730	-0.40	7.99	404	338	0.27
珠穆朗玛峰 Mount Qomolangma	28.21	86.56	4 276	2.50	10.73	282	271	0.10
改则 Gêrzê	32.30	84.08	4 437	0.03	10.39	171	154	0.03
日土 Rutog	33.40	79.72	4 286	0.50	11.64	69	59	0.07

Fig. 1 Relationships between specific leaf area (SLA) and mass-based leaf N concentration (Nmass) in Stipa purpurea of Xizang.

Table 2 Correlation coefficients for linear relationships between climatic factors and leaf functional traits of Stipa purpurea in pooled data across the five study sites

环境因子 Environmental factor	叶性状 Leaf trait
环境因子 Environmental factor	比叶面积 SLA (cm·g^-1)	单位重量叶氮含量 N_mass(mg·g^-1)	单位面积叶氮含量 N_area (g·m^-2)
生长季平均气温 Mean air temperature in growing season (℃)	0.21	-0.29	-0.46^**
年平均气温 Annual mean air temperature (℃)	0.21	-0.27	-0.36^*
生长季降水量 Precipitation in growing season (mm)	0.01	0.20	0.24
年降水量 Annual precipitation (mm)	0.01	0.21	0.28
土壤全氮含量 Total N in soil (mg·g^-1)	0.19	0.18	0.50^**

Fig. 2 Relationships of specific leaf area (SLA) with leaf thickness (A) and leaf density (B) of Stipa purpurea. Trends lines are for the data from the arid and semi-arid areas in Fig. 2A and the semi-humid areas in Fig. 2B, respectively.

Fig. 3 Relationships of (A, B) leaf density and (C, D) leaf thickness of Stipa purpurea with growing season mean temperature and precipitation. Trends lines are for all pooled data.

Fig. 4 Relationships of area-based leaf N concentration (Narea) with leaf density (A) and leaf thickness (B) of Stipa purpurea. Trends lines are for the data from the semi-humid areas.

Fig. 5 Relationships between area-based leaf N concentration (Narea) and aboveground biomass of Stipa purpurea.

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